Do you have trouble with automated programs completing forms on your websites and making cart loads of submissions? Or even just a few spammers submitting their betting ads, performance enhancing pill sites, and share purchase suggestions? And yet you don't want to have to have anyone who wants to use your site register.

Using what has become known as captcha technology, you can display a graphic with some text on what's basically a login page, then have your human user type that text back in. It's very difficult indeed for automata to recongnise the text, and can be doubly so if you vary the background, change fonts between characters and change text colour, scale, rotation. Mind you, you can make it pretty tough for the human too.

You'll find captcha in use already on many big sites, and there are other sites that will host the service for you. Actually, if you've got PHP available and the GD module it's very easy to code it up from first principles and that gives you the ultimate of flexibility.

* Try my demo here
* Show source code of main demo
* Show source code of graphic generator
(written 2006-07-17 09:28:12)

 H999 - Additional PHP Material
A192 - Web Application Deployment - Firewalls
G903 - Well House Consultants - Running and moderating forums
H304 - PHP - DDA, Style and image handling

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Simple polymorphism example - C++
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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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